Apparatus and control method for feeder system for flowable material

ABSTRACT

An apparatus for precisely controlling the feed rate of a feeder comprises: a motor operatively connected to the feeder to cause dispensing of the feeder when the motor is driven; a control circuit for supplying, when actuated, an AC voltage supply to the motor for driving of the motor; a counter disposed in communication with the control circuit for actuation thereof when an overflow signal is generated by the counter; a latch controller disposed in communication with the counter for enablement and disablement of the counter, the latch controller disabling the counter when the overflow signal is generated by the counter; a detector connected to the AC voltage supply for detecting when the AC voltage crosses over a median voltage thereof, the detector further disposed in communication with the latch controller for enablement of the counter when the median voltage is detected; and a fuzzy logic controller disposed in communication with the counter for generating an output to the counter that loads a determined count into the counter such that the counter generates an overflow signal within a time interval equal to a determined percentage of the half period of the AC voltage. The control circuit includes a pair of silicon control rectifiers disposed in parallel but reversed to one another resulting in each silicon control rectifier being able to supply the AC voltage to the motor during opposite half periods of a time period of the AC voltage if continuously actuated.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is entitled to the benefit of, and claimspriority to, U.S. Provisional Patent Application Ser. No. 60/064,812,filed Nov. 7, 1997, by Moran et al., and entitled “CONTROLLER FORVIBRATORY FEED SYSTEM FOR BULK SOLIDS” and U.S. patent application Ser.No. 09/188,402, filed Nov. 6, 1998, by Moran et al., and entitled“APPARATUS AND CONTROL METHOD FOR FEEDER SYSTEM FOR FLOWABLE MATERIAL,”the entirety of which is incorporated herein by reference.

BACKGROUND OF THE PRESENT INVENTION

[0002] The present invention relates broadly to bulk material supplysystems and, more particularly, to a feed system for bulk solids and itsassociated controller wherein the controller employs fuzzy logic forrapid reactions to changes in weight.

[0003] Bulk solids appear throughout industry and must be handled orprocessed in a manner which will provide consistent results withoutwaste. Examples of industries which utilize bulk solids include food,lumber, paper, chemical, petroleum refining, rubber, stone, clay, glass,and concrete. The bulk solid materials may include such diverse items ascabbage flakes, bleach, bauxite, baking soda, fiberglass, flour, grassseed, iron ore, starch, sugar, raisins, parsley, noodles, nylon, mineralfiber, mica, lime, and detergent. All of these materials share a commonfeature in that they are flowable solids. They are fungible materialswhich may be poured for filling into containers or otherwise meteredunder flow conditions for processing.

[0004] Typically, such processing includes providing a hopper filledwith the bulk material with some form of regulator or metering deviceproviding the necessary flow control for processing.

[0005] One method of determining how much bulk solid material has beendispensed during any given dispensing operation is by using theso-called loss-in-weight method. There, the hopper containing the bulkmaterial is continually weighed and the reduction in weight isindicative of the material dispensed.

[0006] Further, the reduction in weight-per-unit time is indicative ofthe rate at which a predetermined amount of the bulk material isdispensed. Therefore, by precisely determining the change in weight ofthe hopper, a precise indication of the amount of material dispensed isrealized. This information can be used for controlling the feed process.Furthermore, while the present invention is described for operation witha vibratory feeder, it should be noted that it is equally effective withscrew feeders or belt feeders. The focus of the present invention liesin its applicability to loss-in-weight feeders.

[0007] A common method which is used to control dispensing of bulksolids is the proportional method used throughout the industry. Thesetpoint for such control method is a desired rate of change of weightfor a supply of the bulk solid. However, because the control variable(the weight change) is the integral of the rate of weight change and notthe rate of weight change itself, the proportional control methodcurrently used in the industry, while reliable, is clumsy and lacks acertain amount of precision.

[0008] Several methods may be used to control the actual feed of thebulk solid material. Valves may be used which are open proportionally oropen for a certain time period. Other methods include the use of a beltfeeder or a screw feeder. A vibratory feeder is disclosed in Peschl U.S.Pat. No. 3,973,703. There, a vibrating tray is disclosed containing anumber of plates in an angular relationship to one another. According tothis method, the bulk material will not flow unless the feeder isvibrated or otherwise agitated in some manner. Such feeders allow forprecise flow with the flow rate being based on the amplitude ofvibration or agitation. This type of feeder can provide accurate flowcharacteristics and can respond rapidly to changing inputs from anassociated excitation motor. The motor is driven responsive to a controlvariable. As discussed above, the current proportional controllers areslow to respond to changes in demand or process changes and, therefore,the precision and rapid changing characteristics of any loss in weighttype feeders including the vibratory feeder are not fully realized usinga proportional controller.

SUMMARY OF THE PRESENT INVENTION

[0009] It is accordingly an object of the present invention to provide afeed control system which precisely controls a vibratory feeder andoffers rapid response to a change in demand.

[0010] Briefly summarized, the method of the present invention includesdetermining an appropriate change to a regulator that controls anoutflow of a flowable material from a supply of the flowable material.The method includes the steps of, for a plurality of small timeintervals during the outflow, (a) calculating average valuesrepresentative of a rate of weight change of the supply of the flowablematerial; (b) calculating average values representative of a rate errorbased on the calculated average values for the rate of weight change andbased on a setpoint value for the rate of weight change; (c) calculatingvalues representative of the change in the rate error based on thecalculated average values for the rate error; and (d) determining avalue representative of an appropriate change to the regulator forcontrolling the outflow by applying fuzzy logic control to thecalculated average values representative of the rate error and thecalculated values representative of the change in the rate error.

[0011] Preferably, the method further comprises weighing the supply ofthe flowable material during the plurality of small time intervals aswell as determining the setpoint value by weighing the outflow of theflowable material.

[0012] The apparatus of the present invention precisely controls thefeed rate of the feeder and itself includes: (a) a motor operativelyconnected to the feeder which causes dispensing of a flowable materialby the feeder when the motor is driven; (b) a control circuitoperatively connected to the motor which provides a voltage supply tothe motor for driving the motor when the control circuit is actuated;(c) a counter disposed in communication with the control circuit foractuating the control circuit after a determined time interval; and (d)a fuzzy logic controller disposed in communication with the counter fordetermining the time interval.

[0013] Preferably, the voltage supply is AC voltage and the determinedtime interval ranges between zero and one-half of a time period of theAC voltage. Furthermore, the apparatus preferably includes a sensordisposed in communication with the fuzzy logic controller for measuringa weight of a supply of flowable material that is dispensed by thefeeder.

[0014] In a feature of the present invention, the control circuitdeactuates at a recurring point in time. Preferably, the recurring pointin time is a crossover of a median voltage of the AC voltage supply.Furthermore, the counter preferably restarts at the recurring point intime as well.

[0015] The preferred embodiment of the apparatus of the presentinvention includes: (a) a motor operatively connected to the feeder tocause dispensing of the feeder when the motor is driven; (b) a controlcircuit for controlling the driving of the motor, the control circuitincluding a pair of silicon control rectifiers disposed in parallel butreversed to one another with each silicon control rectifier operativelyconnected to the motor such that, when each silicon control rectifier isfired, an AC voltage is supplied to the motor and the motor is driven,the parallel and reversed disposition of the silicon control rectifiersin the control circuit resulting in each silicon control rectifier beingable to supply the AC voltage to the motor during opposite half periodsof a time period of the AC voltage; (c) a counter disposed incommunication with each of the silicon control rectifiers for actuationthereof when an overflow signal is generated by the counter; (d) a latchcontroller disposed in communication with the counter for enablement anddisablement of the counter with the latch controller disabling thecounter when the overflow signal is generated by the counter; (e) adetector connected to the AC voltage for detecting when the AC voltagecrosses over a median voltage thereof with the detector being furtherdisposed in communication with the latch controller, with the detectorgenerating a signal to the latch controller for enablement of thecounter when the median voltage is detected; (f) a fuzzy logiccontroller disposed in communication with the counter for generating anoutput to the counter that loads a determined count into the countersuch that the counter generates an overflow signal within a timeinterval equal to a determined percentage of the half period of the ACvoltage, whereby each silicon control rectifier is fired for thedetermined percentage of the half period of the AC voltage, the counterretaining the determined count until a different determined count isloaded into the counter by the fuzzy logic controller; (g) a sensor thatmeasures a weight of a supply of flowable material that is dispensed bythe feeder for calculation of a rate of weight change of the supply offlowable material; and (h) a second sensor disposed for measurement of aweight of the flowable material dispensed by the feeder and a timeinterval of the dispensing for calculation of a setpoint value.

[0016] Furthermore, the fuzzy logic controller includes ananalog-to-digital converter, a moving average filter, and a fuzzy logicprocessor including a predetermined rule base, whereby the fuzzy logiccontroller compares the rate of weight change of the supply of flowablematerial and the setpoint value for determination of the percentage ofthe half period of the AC voltage before the controller generates theoverflow signal.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017]FIG. 1 is diagrammatic view of a bulk material handling systememploying a controller according the preferred embodiment of the presentinvention;

[0018]FIG. 2 is a block diagram of the external components of the feedercontrol system; and

[0019]FIG. 3 is a block diagram of the fuzzy logic processor.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0020] According to the present invention, a controller is providedwhich uses fuzzy logic reasoning to provide control signals to siliconcontrol rectifiers (SCRs) which drive an electric motor that causesvibration of the feeder for dispensing bulk solids.

[0021] To that end, the present invention provides a fuzzy logic basedprocessor which produces an output signal for controlling the firing ofa pair of SCRs which control through a motor the excitation of avibratory feeder for feed rate control when dispensing bulk solidmaterial. The system employs a hopper which is suspended on load cells.The hopper contains a predetermined amount of bulk solid material fordispensing and is replenished from a material supply in a controlledmanner. In reality, the combined weight of the electromagnetic drivemotor, feed tray, hopper, suspended components and material is weighedusing the load cells with all weight except for the material “zeroedout” electronically.

[0022] The output from the load cells is sent to the controller and,initially, to an anti-aliasing filter. High frequencies, which in analogcontrollers normally are effectively eliminated by the low passfiltering, may because of “aliasing” appear as low frequency signals inthe bandwidth of the sample control system. The anti-aliasing filtereffective eliminates all signal components with frequencies above halfthe sampling frequency. From there, the signal is fed to an analog todigital converter which is Preferably an oversampling sigma-delta typeof charge balancing converter. The output of the converter enters aprogrammable digital filter with notch frequencies of the filter set to5, 10, 25, 30, 50, or 60 hertz depending on the controller. Analog todigital conversion occurs at a rate that is a function of notchfrequency. The rate may be expressed as time=1/notch frequency. Theoutput code from the filter results in a converted signal of 24 bitswith no missing codes and 0.0015% nonlinearity. This corresponds to afull-scale count of 16,777,216 before post filtering. The software readsa 24-bit word at a rate equal to the notch frequency for which theprogrammable filter has been set. The software then places this countinto two moving average filters, one for use by the display and one tobe used by the control algorithm. A number of averages for each postfilter is entered independently. In general, a small number of averagesin the control filter allows for fast, tight control and a larger numberin the display filter allows for more readable display of rate output.

[0023] Analog to digital conversion occurs every 100 millisecondsprovided the notch frequency is 10 Hz, with a digital count representingthe combined weight of the hopper, feeder, and material being dispensed.A 5 Hz notch frequency will result in a conversation rate of 200milliseconds. The digital count is stored in a circular ring bufferwhich is used to average the weight. The number of counts to be averagedequals the number of filter samples. The ring buffer stores apredetermined number of samples. As each new sample is introduced, theoldest sample in residency is subtracted from the running total and thenewest sample is added to the running total with the average count beingcomputed by dividing the running total by the number of filter samples.

[0024] This average count is then converted to a weight value bysubtracting the tare count, which amounts to deducting the weight of thecontainer and everything supported by the load cells except for thematerial, and then multiplying the difference by the weight to countratio which was predetermined during calibration. The change in weightis computed by subtracting the current weight from the previouslymeasured weight, with the current weight being stored as the newprevious weight. Rate is computed by multiplying the change in weightvalue by the rate per minute factor. The rate is stored in a circularring buffer which is used to provide an average in a manner discussedpreviously.

[0025] The computer then undertakes fuzzy logic processing based on thechange in weight and the rate of weight change. The frequency ofperforming the fuzzy logic processing is controlled by an update valuewhich is entered by the operator and is a multiple of 100 milliseconds.This time period is also a function of the notch frequency. As is knownwith fuzzy logic, a rule base is provided and appears as follows:

[0026] The fuzzy logic rule base has two inputs. One is the rate errorand the other is the change in rate error since last processing cycle.The rate error is determined by subtracting the calculated change inweight from the measured change in weight with the calculated change inweight being computed from the rate setpoint, the rate per minutefactor, and the frequency of the fuzzy logic processing cycle. Thechange in rate error is computed by subtracting the previous rate errorfrom the current rate error. The current rate error is then stored asthe new previous rate error.

[0027] Basically, the analysis of the rate error and the change in rateerror proceeds in four steps. Under fuzzification, the membershipfunctions defined on the input variable are applied to their actualvalues, to determine the degree of truth for each rule premise. Underinference, the truth value for the premise of each rule is computed, andapplied to the conclusion parity of each rule. This results in one fuzzysubset to be assigned to each output variable for each rule. The outputmembership function is scaled by the rule premise's computed degree oftruth.

[0028] Under composition, all of the fuzzy subsets assigned to eachoutput variable are combined together to form a single fuzzy subset foreach output variable. Using MAX-DOT inference, the combined output fuzzysubset is constructed by taking the pointwise maximum over all of thefuzzy subsets assigned to variables by the inference rule. Finally, thepresent invention employs centroid defuzzification, which is used toconvert the fuzzy output set to a crisp number. The crisp number maythen be employed to control the vibration of the feeder. In the centroidmethod, the crisp value of the output variable is computed by findingthe variable value of the center of gravity of the membership functionfor the fuzzy value. The present fuzzy logic rule base produces anoutput which is a percentage value. The output is then multiplied by thegain value. The resulting value is algebraically added to the SCRpercent value by the computer, which directly controls the firing of theSCRs. The firing of the SCRs controls the electromagnetic drive motor.

[0029] The membership functions are as follows:

[0030] Membership Function—Rate Error:

[0031] Range of input is −1 to +1.

[0032] Member negative points are −1,1 −0.5,1 0,0

[0033] Member zero points are −0.5,0 0,1 0.5,0

[0034] Member positive points are 0,0 0.5,1 1,1

[0035] Membership Function—Change in Rate Error:

[0036] Range of input is −1 to +1.

[0037] Member negative points are −1,1 −0.5,1 0,0.

[0038] Member zero points are −0.5,0 0,1 0.5,0

[0039] Member positive points are 0,0 0.5,1 1,1

[0040] Membership Function—Output Change Percentage:

[0041] Range of output is −1000 to +1000.

[0042] Membership negative points are −1000,0 −833.33,1 −666.66,0

[0043] Membership zero points are −166.66,0 0,1 166.66,0

[0044] Membership positive points are 666.66,0 833.33,1 1000,0

[0045] The rule base contains nine rules which follow:

[0046] 1. If rate error is N and change in rate error is N, then outputchange percentage is P.

[0047] 2. If rate error is N and change in rate error is Z, then outputchange percentage is P.

[0048] 3. If rate error is N and change in rate error is P, then outputchange percentage is N.

[0049] 4. If rate error is Z and change in rate error is N, then outputchange percentage is P.

[0050] 5. If rate error is Z and change in rate error Z, output changepercentage is Z.

[0051] 6. If rate error is Z and change in rate error is P, then outputchange percentage is N.

[0052] 7. If rate error is P and change in rate error is N, then outputchange percentage is P.

[0053] 8. If rate error is P and change in rate error is Z, then outputchange percentage is N.

[0054] 9. If rate error is P and change in rate error is P, then outputchange percentage is N.

[0055] In the above rule base, P represents positive, N representsnegative, and Z represents zero.

[0056] The main algorithm for the MAX-DOT centroid method for fuzzyinterfacing is as follows:$V = {\sum\limits_{i = 1}^{n}{\alpha_{1}{M_{1}/{\sum\limits_{i = 1}^{n}{\alpha_{1}A_{1}W_{1}}}}}}$

[0057] where:

[0058] V is the variable value at the centroid of the fuzzy set,

[0059] α_(i): is the degree of membership computed for the premise ofrule i,

[0060] W₁ is the weight assigned to the rule i,

[0061] M₁ is the moment of the membership function assigned to V in rulei around zero, and

[0062] A₁ is the area of the membership function assigned to V in rulei.

[0063] The electromagnetic drive motor, which controls the vibration ofthe feeder, requires an input of between 0 and 115 VAC for correspondingamplitudes of vibration between 0% and 100% (corresponding to 0.000inches to 0.060 inches). The SCR drive control works by turning on theSCRs for a percentage of each half cycle of the AC line voltage. In fullwave control an SCR is needed for each polarity of a line, this beingaccomplished by placing two SCRs in parallel with one reverse from theother. If each SCR conducts for half of its corresponding half cycle,50% of the line voltage is the average voltage sent to the load. Once anSCR is turned on, the SCR stays on until the current flowing through itdrops to 0, i.e., when the AC line reverses polarity.

[0064] The control circuit includes a “zero crossing detector”. Thiscircuit generates a narrow pulse at each crossing of zero volts of theAC line voltage. This occurs every 8.33 milliseconds for a 60 cycleline. When the zero crossing pulse occurs, it sets a latch whose outputenables the 16 bit counter to count. The counter is clocked by a crystaloscillator at 7.3728 MHz. If the counter had a net count of zero when itwas enabled, it would take 65536 counts of the clock to fill the counterand generate an overflow. With a clock of 7.3728 MHz, each cycle is 135nanoseconds. Therefore, the 65536 counts×135 nanoseconds=8.888milliseconds or little more time than one-half of the AC cycle. If asmall count of 4500 is loaded into the counter, the first clock pulseafter zero crossing enables the counter and it will take almost theentire half cycle for an overflow to occur. This overflow signal doestwo things. Initially, it triggers the SCRs. It also resets the controllatch disabling the counter until the next zero crossing. The firing ofan SCR just before zero crossing results in an average output voltage ofalmost zero volts. This happens every 8.333 milliseconds without anyintervention from the software. If a large count is loaded into thecounter, e.g., 64,000, the SCRs are turned on just after the zerocrossing and the output voltage will approximate the line voltage. Theseminimum and maximum counts are scaled in the software to be 0% to 100%output. Using this method of triggering the SCRs, minimum softwareintervention is required because if the output does not need to changethe software need do nothing. The circuit runs by itself. If the outputneeds to change, the software writes the new number once and the outputis changed at the next zero crossing.

[0065] By employing the fuzzy logic controller in combination with thezero crossing detector, the software can cooperate with the zerocrossing detector to rapidly change the firing rate of the SCRs therebycontrolling the feeder in a precise manner.

[0066] Turning now to the drawings and, more particularly to FIG. 1, abulk material handling system is generally indicated at 10 and includesa skeletal frame 12 supporting the components of the system. A productconveyor 16 is formed as a driven, endless belt system for carrying afungible, flowable product P (such as strawberries) on the top flightthereof. The product P is emitted from a feeder conveyor 14 disposed atone end of the product conveyor 16. A series of idlers 38 supports thetop flight of the conveyor 16. The product conveyor 16 conveys theproduct P through the handling system. A 5 hopper 18 is formed as aninverted, frusto-conical member having a replenishment feeder 23 at anopen, upper end thereof. A vibrational distribution feeder 30 isdisposed at the lower, open end of the hopper 18 at a position spaced apredetermined distance from the product conveyor 16 for depositing bulkmaterial B (such as sugar) on the product P on the conveyor 16. Thevibrational feeder 30 includes an electromagnetic drive motor 32 beingcontrolled by two silicon controlled rectifiers (SCRs) contained withina SCR controller illustrated generally at 34. The replenishment feeder23 is controlled by a refill gate 24 operationally attached thereto. Thehopper 18 is suspended on load cells 20 by cables 22.

[0067] The present invention also includes two microprocessor orcomputer-based controls. Initially, a weight speed multiplier 44 ismounted to the frame 12 and operatively connected to a load cell 45associated with one of the idlers 38 in contact with the productconveyor 16 to determine the amount of bulk material dispensed and timeof the dispensing.

[0068] A second computer-based control is the rate controller 40 andreceives input from the operator and, through other various other inputsas will be discussed in greater detail hereinafter, controls firing ofthe SCRs to excite the electromagnetic drive motor 32 to control thevibrational feeder 30. The rate controller 40 receives input from theweight speed multiplier 44 to coordinate the operation of thevibrational feeder 30 with the operation of the product conveyor 16. Anelectrical output signal is supplied through control lines 26 from therate controller 40 to the refill gate 24 to replenish the hopper 18 whenthe bulk material supply gets low. The rate controller 40 receives anelectrical signal from the load cells 20 through electric line 28 fromwhich the rate error and change in rate error are determined. An outputline extends from the rate controller 40 to the SCR controllers 34 forcontrolling the vibrational feeder 30.

[0069] The external arrangement can also be seen in FIG. 2. There, in ablock form, it can be seen that controller 40 is operationally connectedto the load cells 20 through control line 28. The load cells 20 arephysically connected to the hopper 18. The hopper/load cell arrangementprovides the primary input to the fuzzy logic controller 40.Additionally, the weight speed multiplier 44 supplies a coordinatingsignal (the setpoint) through electric line 43 to the rate controller40. The output of the rate controller 40 is transmitted throughelectrical line 36 to the SCR controller 34 including two SCRs 46,48which excite the drive motor 32 for operating the vibrating feeder 30.

[0070] Turning now to FIG. 3, the internal processor is illustratedgenerally in broken lines at 50. The output from the load cells 20 isadministered to an anti-aliasing filter 54 which acts to remove aliasesof the primary frequency of interest. The anti-aliasing filter 54 sendsits output signal to an analog/digital converter 56 which provides adigital output for processing by the fuzzy logic controller. The digitaloutput signal is fed to the ring buffers 58 and the output of these isthe rate error 60 and the change in rate error 62 which are fed to thefuzzy logic rule base 52 for processing with the output appearing onoutput signal line 64.

[0071] In operation, the conveyor 16 is moved under the vibratory feeder30 and receives bulk material from the hopper according to controlledvibrations of the vibrating feeder 30. The load cells 20 monitor thechange in weight and continually feed this information along lines 28 tothe main controller 40. Meanwhile, the weight speed multiplier 44 isreceiving input from the load cell 45 associated therewith regardingspeed and weight carried on the top flight of the conveyor 16. Theoutput of the main load cells 20 is processed using the anti-aliasingfilter 54, the analog to digital converter 56, and the ring buffers 58to arrive at a value for the rate error 60 and a value for the rate ofchange of the weight error 62. Mapping of these values 60,62 are madeaccording to fuzzy logic membership functions and the results areapplied to a fuzzy logic controller comprising a rule base 52 within therate controller 40, and the output variable appears as a control signal64 which controls the firing of the SCRs which, in turn, controls therate at which the vibrational feeder dispenses bulk material product.

[0072] The above system provides a rapid and precise apparatus forcontrolling the amount of bulk solid material distributed during aprocess.

[0073] Moreover, it is contemplated within the scope of the presentinvention that, while less precise, a single SCR could be used in thecontrol circuit, whereby dead time would occur during each cycle when novoltage could be applied to the motor. Furthermore, it is alsocontemplated that, while the control circuit described in the preferredembodiment includes two SCRs disposed in parallel, reversedconfiguration, other electronic components can be used such as diodesand transistors with the desired result.

[0074] It will therefore be readily understood by those persons skilledin the art that the present invention is susceptible of broad utilityand application. Many embodiments and adaptations of the presentinvention other than those herein described, as well as many variations,modifications and equivalent arrangements will be apparent from orreasonably suggested by the present invention and the foregoingdescription thereof, without departing from the substance or scope ofthe present invention. Accordingly, while the present invention has beendescribed herein in detail in relation to its preferred embodiment, itis to be understood that this disclosure is only illustrative andexemplary of the present invention and is made merely for purposes ofproviding a full and enabling disclosure of the invention. The foregoingdisclosure is not intended or to be construed to limit the presentinvention or otherwise to exclude any such other embodiments,adaptations, variations, modifications and equivalent arrangements, thepresent invention being limited only by the claims appended hereto andthe equivalents thereof.

What is claimed is:
 1. A method of determining an appropriate change toa regulator that controls an outflow of a flowable material from asupply of the flowable material, comprising the steps of: for aplurality of small time intervals during the outflow, (a) calculatingvalues representative of a rate of weight change of the supply of theflowable material based on weight measurements taken over said smalltime intervals; (b) calculating values representative of a rate errorbased on said calculated values for the rate of weight change and basedon a setpoint value for the rate of weight change; (c) determining avalue representative of an appropriate change to the regulator formaintaining the outflow at the setpoint value for the rate of weightchange by applying fuzzy logic control to said calculated valuesrepresentative of the rate error.
 2. The method of claim 1 , furthercomprising calculating values representative of the change in the rateerror based on said calculated values for the rate error, and applyingfuzzy logic control to said calculated values representative of thechange in the rate error.
 3. The method of claim 1 , wherein saidcalculated values representative of a rate of weight change are averagevalues.
 4. The method of claim 1 , wherein said calculated valuesrepresentative of a rate error are average values.
 5. The method ofclaim 1 , further comprising weighing the supply of the flowablematerial during the plurality of small time intervals.
 6. The method ofclaim 1 , further comprising determining the setpoint value by weighingthe outflow of the flowable material from the supply of the flowablematerial.
 7. An apparatus for precisely controlling the driving of amotor, comprising: (a) a control circuit operatively connected to themotor which provides a voltage supply to the motor for driving the motorwhen the control circuit is actuated; (b) a timing circuit disposed incommunication with said control circuit for actuating said controlcircuit after a determined time interval; (c) a fuzzy logic controllerdisposed in communication with said timing circuit for determining saidtime interval; and (d) a sensor disposed in communication with saidfuzzy logic controller for measuring a rate of a supply of flowablematerial that is dispensed by the feeder.